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A quick follow-up to my post from a few days ago about the study suggesting that being overweight as you age doesn’t predict longer life after all. Several people have pointed out the just-released studies on the Edmonton Obesity Staging System (press release here; one of the abstracts here), which found that:
Obese individuals with no, or only mild, impairments were found to have the same mortality risk as lean individuals, and were less likely to die from cardiovascular causes.
Does this mean that being a little bit overweight doesn’t hurt, and may even help — contradicting the Loma Linda study I wrote about earlier? Not exactly. The studies are looking at two different things.
The Edmonton Obesity Staging System (EOSS) is summarized in this graphic. Basically, Stage 0 means you’re overweight but have no signs of any related risk factors like hypertension, impaired fasting glucose, elevated liver enzymes, etc. Stage 1 means you’re overweight but only have subclinical indications of any of these related risk factors. Only once you get to Stage 2 do you start dealing with problems like hypertension and Type 2 diabetes.
What the latest study found is that being Stage 0 or 1 didn’t predict earlier death than having “normal” weight. This is entirely consistent with the last two decades of research by Steven Blair (one of the authors of the new study) on “fatness versus fitness.” The basic gist is that fatness, on its own, isn’t what kills you. If you’re overweight but can avoid the risk factors commonly associated with being overweight — and the main way to do that, Blair argues, is to be aerobically fit — then your health outcomes are no different than the average person.
The Loma Linda study, on the other hand, didn’t separate out the “fat and fit” people from the “fat and unfit.” They just looked at the overall results based on BMI, and found that those who were overweight were more likely to die earlier. This isn’t unexpected — because let’s face it, those who are overweight are more likely (but not guaranteed) to have associated risk factors like hypertension and diabetes.
To make a slightly silly analogy, we could say that the Loma Linda study is equivalent to showing that people who buy cigarettes are more likely to get cancer. Of course, this doesn’t mean that the act of purchasing them gives you cancer — it’s perfectly possible to buy cigarettes and not smoke them. But those who buy them are generally pretty likely to smoke them. (NOTE: this was the simplest analogy I could think of — I’m not equating obesity to smoking, not am I saying that being “fat and fit” is as rare as buying cigarettes and not smoking them!)
So why does this matter? Well first, I should emphasize that I think Steven Blair (and Arya Sharma and their colleagues)’s message is very important. Our public health messages should focus on fitness, not fatness. So — as I concluded my previous post by saying — I don’t think the Loma Linda results “prove” that being overweight is a ticking time bomb. Instead, it’s the opposite message that I’m emphasizing: that not being overweight isn’t something you should worry about. The earlier studies suggesting that being overweight made you live longer led to media articles like Margaret Wente’s infamous “Get fat, live longer” — and that’s misleading. The Loma Linda study corrects that mistake.
And on that note, I should point out that same false comparison is being made to some degree with the new study. For example, the passage I quoted above: “Obese individuals with no, or only mild, impairments… were less likely to die from cardiovascular causes [compared to lean individuals].” (Or even worse, this press release that sums up the study as finding that “being fat can actually be good for you.”) This is a false comparison. They’re cherry-picking the subset of overweight people who have no clinical signs of any risk factors like hypertension or blood sugar problems, and comparing them to all lean people, however healthy or unhealthy. This doesn’t tell us that it’s “good” to be overweight — it tells us that (duh) it’s good not to have diabetes, high blood pressure, arthritis and a messed-up liver!